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>Chapter 41. PL/Perl - Perl Procedural Language</TD
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><H1
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><A
NAME="PLPERL-TRUSTED"
>41.5. Trusted and Untrusted PL/Perl</A
></H1
><P
>   Normally, PL/Perl is installed as a <SPAN
CLASS="QUOTE"
>"trusted"</SPAN
> programming
   language named <TT
CLASS="LITERAL"
>plperl</TT
>.  In this setup, certain Perl
   operations are disabled to preserve security.  In general, the
   operations that are restricted are those that interact with the
   environment. This includes file handle operations,
   <TT
CLASS="LITERAL"
>require</TT
>, and <TT
CLASS="LITERAL"
>use</TT
> (for
   external modules).  There is no way to access internals of the
   database server process or to gain OS-level access with the
   permissions of the server process,
   as a C function can do.  Thus, any unprivileged database user can
   be permitted to use this language.
  </P
><P
>   Here is an example of a function that will not work because file
   system operations are not allowed for security reasons:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION badfunc() RETURNS integer AS $$
    my $tmpfile = "/tmp/badfile";
    open my $fh, '&gt;', $tmpfile
        or elog(ERROR, qq{could not open the file "$tmpfile": $!});
    print $fh "Testing writing to a file\n";
    close $fh or elog(ERROR, qq{could not close the file "$tmpfile": $!});
    return 1;
$$ LANGUAGE plperl;</PRE
><P>
    The creation of this function will fail as its use of a forbidden
    operation will be caught by the validator.
  </P
><P
>   Sometimes it is desirable to write Perl functions that are not
   restricted.  For example, one might want a Perl function that sends
   mail.  To handle these cases, PL/Perl can also be installed as an
   <SPAN
CLASS="QUOTE"
>"untrusted"</SPAN
> language (usually called
   <SPAN
CLASS="APPLICATION"
>PL/PerlU</SPAN
>).
   In this case the full Perl language is available.  When installing the
   language, the language name <TT
CLASS="LITERAL"
>plperlu</TT
> will select
   the untrusted PL/Perl variant.
  </P
><P
>   The writer of a <SPAN
CLASS="APPLICATION"
>PL/PerlU</SPAN
> function must take care that the function
   cannot be used to do anything unwanted, since it will be able to do
   anything that could be done by a user logged in as the database
   administrator.  Note that the database system allows only database
   superusers to create functions in untrusted languages.
  </P
><P
>   If the above function was created by a superuser using the language
   <TT
CLASS="LITERAL"
>plperlu</TT
>, execution would succeed.
  </P
><P
>   In the same way, anonymous code blocks written in Perl can use
   restricted operations if the language is specified as
   <TT
CLASS="LITERAL"
>plperlu</TT
> rather than <TT
CLASS="LITERAL"
>plperl</TT
>, but the caller
   must be a superuser.
  </P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>    While <SPAN
CLASS="APPLICATION"
>PL/Perl</SPAN
> functions run in a separate Perl
    interpreter for each SQL role, all <SPAN
CLASS="APPLICATION"
>PL/PerlU</SPAN
> functions
    executed in a given session run in a single Perl interpreter (which is
    not any of the ones used for <SPAN
CLASS="APPLICATION"
>PL/Perl</SPAN
> functions).
    This allows <SPAN
CLASS="APPLICATION"
>PL/PerlU</SPAN
> functions to share data freely,
    but no communication can occur between <SPAN
CLASS="APPLICATION"
>PL/Perl</SPAN
> and
    <SPAN
CLASS="APPLICATION"
>PL/PerlU</SPAN
> functions.
   </P
></BLOCKQUOTE
></DIV
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>    Perl cannot support multiple interpreters within one process unless
    it was built with the appropriate flags, namely either
    <TT
CLASS="LITERAL"
>usemultiplicity</TT
> or <TT
CLASS="LITERAL"
>useithreads</TT
>.
    (<TT
CLASS="LITERAL"
>usemultiplicity</TT
> is preferred unless you actually need
    to use threads.  For more details, see the
    <SPAN
CLASS="CITEREFENTRY"
><SPAN
CLASS="REFENTRYTITLE"
>perlembed</SPAN
></SPAN
> man page.)
    If <SPAN
CLASS="APPLICATION"
>PL/Perl</SPAN
> is used with a copy of Perl that was not built
    this way, then it is only possible to have one Perl interpreter per
    session, and so any one session can only execute either
    <SPAN
CLASS="APPLICATION"
>PL/PerlU</SPAN
> functions, or <SPAN
CLASS="APPLICATION"
>PL/Perl</SPAN
> functions
    that are all called by the same SQL role.
   </P
></BLOCKQUOTE
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